Guest Anonymous Posted February 27, 2002 Share Posted February 27, 2002 I'm re-posting this because I only received one answer in the carb group. Since more people read this board, maybe someone has experienced this problem... Hi, I'm new to this board, and over the past few weeks I've been reading many interesting posts and replys. I purchased a hybrid Z car last summer. It's a '77 280z with a mid-70s Chevy 350, 3 speed automatic, mild cam, AFB 600 carb, and Holley electric fuel pump. My problem is that my car is very prone to stumbling and flooding. I installed a fuel regulator between the fuel pump and carb, but the adjustment on the regulator doesn't seem to affect the pressure. (I installed a fuel pressure gauge on the regulator) I'm reading over 12 pounds of fuel pressure, which I know is about 6 pounds too high. I think that the carb needs about 6 pounds of pressure, else the excessive pressure floods the fuel bowls. Does the regulator need a fuel return back to the gas tank to work properly? If so, I don't see a connection on the regulator to make it work. I notice that when I screw the gas cap on all the way, the pressure in the gas tank really builds up. Upon loosening the cap, the pressure comes out with a whoosh! When I keep the cap loose, the stumbling and flooding problems are less severe. Should I drill a small hole in the fuel cap to permanently keep the fuel tank de-pressurized? After all, this high pressure is not needed since I don't have fuel injection. Sorry for the long post, but I wanted to see if anyone else has had the same problem, and if so, how they cured it. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted February 27, 2002 Share Posted February 27, 2002 look here, http://www.centuryperformance.com/fuel.asp and yes you need a fuel return line, how most fuel pressure regulators work is by allowing an fuel over a set pressure to flow through them so what you do is feed fuel to the carb but just before the carb (tee/split)the fuel line so that all the fuel can return to the tank but first must pass through the pressure regulator , this insures at least the pressure you set the regulator to will be available at the carb inlet because the regulator will not allow fuel to return to the tank at any less than that pressure, yet all fuel over that pressure is free to return to the tank (this keeps that carb inlet fuel at the set pressure reading.) Quote Link to comment Share on other sites More sharing options...
Guest super280z Posted February 27, 2002 Share Posted February 27, 2002 it also sounds like you're tank might not be vented properly. might check into that. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted February 27, 2002 Share Posted February 27, 2002 Hi, I have a fuel regulater and gauge on my edelbrock set to 5 psi. I do not have a return line hooked up. I blocked mine going back to the fuel tank. I also build a little pressure in the tank, but is not a problem. My car runs perfectly like this and I think if you were to get a better regulater yours might also. The rgulater should not need any kind of return line in order to function. Just my 2 cents worth, but mine is funtioning like I stated. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted February 27, 2002 Share Posted February 27, 2002 Ziggy if your regulator works fine with no return line your fuel pump is most likely putting out less than 7 psi at the carb, a fuel return line almost always makes the system work more effeciently and if your pump puts out over 10 psi at the carb location its almost mandatory. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted February 28, 2002 Share Posted February 28, 2002 Hi Grumpyvette, I am not sure how many psi the pump produces , it is a factory fuel pump in my 87 suburban. I have converted the sub to non computer, and did not change the factory pump. I just put in an in line fuel pressure gauge and a small gauge and plugged the return line under the chasis. I'm not an expert, I just tried it and it worked for me. I rebuilt the engine from a junkyard set that I bought. It was the first engine I have ever rebuilt. It was a hoot to hear it fire up and run. I have less than 1500 miles on it now and it seems to run very well. I'm new so forgive my lack of knowledge. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted February 28, 2002 Share Posted February 28, 2002 Grumpyvette and Ziggy, Thanks for your replies and comments. Grumpy, I read over the article that you supplied the link for (above), and it mentioned that there are two types of regulators, the type that has a return line, and the type called a 'deadhead' which has no return line. I believe that the type I have is the deadhead type. This coming weekend I'm going to crawl under the car to see if I can locate the fuel pump and determine more about it. There are apparently 3 types of Holley electric fuel pumps. It might be helpful if I knew more about what kind of pump I have (I didn't do the conversion myself). It may be that I have the wrong kind of regulator installed and it's not a good match for my fuel pump. I'm going to have to research this more. Like you have mentioned, "do the research before you buy the parts." Looks like you're right on in this advice! Regarding the pressure build up in the fuel tank, it sure seems excessive. Does my idea of drilling a tiny hole in the fuel cap make any sense, or is this a bad idea? Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted February 28, 2002 Share Posted February 28, 2002 altho the smog police wont like it much venting the tank will help. and yes there are two types of regulators but after years of trying to get consistent fuel pressure with the dead head type (with no success) and always haveing flawless performance useing the return line type ,I just use those.on high performance cars a 3/8" feed /5/16" return line minimum works, on any car thats raced 1/2"feed,3/8" return lines are almost mandatory.I gave up on manual fuel pumps also as a good high voluum electric fuel pump is much superior. Quote Link to comment Share on other sites More sharing options...
72zcar Posted May 6, 2003 Share Posted May 6, 2003 and yes you need a fuel return line, how most fuel pressure regulators work is by allowing an fuel over a set pressure to flow through them so what you do is feed fuel to the carb but just before the carb (tee/split)the fuel line so that all the fuel can return to the tank but first must pass through the pressure regulator , this insures at least the pressure you set the regulator to will be available at the carb inlet because the regulator will not allow fuel to return to the tank at any less than that pressure, yet all fuel over that pressure is free to return to the tank (this keeps that carb inlet fuel at the set pressure reading.) grumpyvette: I have the holley blue pump and the regulator that came with it... but can not get a steady reading on my gauge. Can I use the regulator that came with the holly blue http://store.summitracing.com/partdetail.asp?part=HLY%2D12%2D802%2D1 to do what you described above? What you said makes alot of sense. thanks, Bob Quote Link to comment Share on other sites More sharing options...
QWKDTSN Posted May 6, 2003 Share Posted May 6, 2003 72zcar, if you want to return fuel to the tank you can't use the stock Holley Blue regulator. However, I have been using the Blue pump and regulator set at just under 6PSI with zero problems. The gauge reads very steadily. Are you sure you have your fuel pump hooked up correctly? You might be getting some kind of fluctuating voltage (bad ground maybe?) Although it is not necessary to run a return, I guess it is a more efficient way of doing it. In my case it's not necessary and it made it a lot easier to run my fuel line by running a single line from the tank up to the engine without having to run a return back. If I were running a more potent engine I'd probably do it differently. Quote Link to comment Share on other sites More sharing options...
72zcar Posted May 6, 2003 Share Posted May 6, 2003 One minute its at 6-7 pounds and then I pull over and look and its at 2-3. why is it doing that? I have the pump in the back and the regulator on the firewall. Feed in through the bottom of regulator and out the right side, left side blocked. from there into a fuel filter and then to a gauge then to the edelbrock 600. Does this sound right? Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted May 6, 2003 Share Posted May 6, 2003 That sounds right on to me. That is how mine is set up as well. 6 lbs with a holley 750 dp. I have heard that edelbrocks should not be given more than 5.5 lbs pressure max. Check your edelbrock manual or go to there site. Mike Quote Link to comment Share on other sites More sharing options...
QWKDTSN Posted May 7, 2003 Share Posted May 7, 2003 That is how mine is set up too, except the fuel filter is mounted before the regulator, not after. This shouldn't affect it, though... My carb is a 650 DP. Quote Link to comment Share on other sites More sharing options...
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